The present invention pertains to the field of manufacture of diagnostic test elements. Specifically, the invention relates to a diagnostic test element for determining an analyte comprised in a body fluid sample, said test element comprising at least one test field with at least one detection layer and at least one separation layer, wherein said at least one separation layer comprises dispersed SiO2 in an amount of about 1.0 to 1.6 g/m2. The invention also relates to a coating composition being capable of forming a separation layer on a diagnostic test element of the present invention described above. Moreover, provided is a method for the manufacture of the diagnostic test element as well as the use of the diagnostic test element for determining the amount of an analyte, preferably, glucose, in a sample of a subject.
In the prior art, numerous diagnostic test elements are known which can be used for detecting an analyte in a sample of a body fluid. The said analyte can be, for example, a metabolite such as glucose. Qualitative and/or quantitative detection of the analyte can be carried out. Known analytes are, for example, glucose, more particularly blood glucose, uric acid, ethanol, and/or lactate. Other types of analytes are also alternatively or additionally detectable. The body fluid can be, for example, whole blood, blood plasma, interstitial fluid, saliva, urine, or other types of body fluids. The invention will now, without restricting further possible embodiments, be described essentially with reference to the detection of glucose in whole blood.
Diagnostic test elements, in principle, comprise at least one detection reagent for the qualitative and/or quantitative detection of the analyte. A detection reagent is to be generally understood to mean a chemical substance or a mixture of chemical substances which, in the presence of the at least one analyte, changes at least one detectable property, more particularly a physically and/or chemically detectable property. Preferably, this property change occurs specifically only in the presence of the at least one analyte to be detected, but not in the presence of other substances. However, in practice, it is possible to tolerate an unspecific property change within certain limits, in the presence of other chemical substances whose presence in the sample of the body fluid is generally unlikely and/or which are present at only a very low concentration.
The at least one property change can be, for example, the change in an optically detectable property, more particularly a color change. Examples of diagnostic test elements having optical detection reagents are well known in the prior art. For example, DE 196 29 656 A1, DE 196 29 657 A1, WO 2010/052306 or EP 0 821 234 B1 describe diagnostic test supports for determining an analyte from whole blood by means of a reagent system which is present in the support and which includes a color formation reagent. Such a diagnostic test support comprises a test field with a sample loading side, onto which the sample is added, and a detection side, on which an optically detectable change occurs as a result of the reaction of the analyte with the reagent system. The test field is configured such that the erythrocytes present in the sample do not reach the detection side. Furthermore, the test field has a transparent slide and a first film layer and also a second film layer applied to the first film layer. The first layer located on the transparent slide is in a moist state and thereby exhibits considerably less light scattering than the second layer lying over it. The first film layer comprises a filler whose refractive index is close to the refractive index of water, whereas the second layer contains a pigment having a refractive index of at least or even >2.0, more particularly of at least 2.2, at a concentration of at least 25% by weight or even more than 25% by weight, based on the dried second layer. For example, the first layer can comprise a sodium aluminum silicate as filler.
However, in practice, the test elements known from the prior art, more particularly test elements having at least one test field, have disadvantages and technical challenges. Since the composition of the film layers may vary from batch to batch, variations may also occur during measurements, e.g., due to remission variation. Currently, batch specific calibration curves are provided as so called “ROM Keys” in electronic format in order to allow for a precise measurement of the analyte. However, it is a rather cumbersome measure for the practitioner to apply an individual calibration curve for each and every batch. Moreover, there is a risk for using wrong calibration curves due to confusions.
A possibility which is currently realized to avoid confusions and additional work for exchanging the ROM-Key comprising the calibration curve is storing the calibration information for the diagnostic test elements on each element or on a magazine comprising a plurality of test elements from the same batch. However, this measure is cost intensive and requires extra production steps since each test element needs to be labeled by, e.g., a bar code or test elements of one batch need to be stored in a bar code labeled magazine.
However, there is a need for less cost intensive measures for safeguarding measurement qualities of the diagnostic test elements which can be realized without the need for additional production steps.